1. Field of the Invention
The present invention relates to a process and an apparatus for determination of the quality of a crimped connection between a conductor and a contact. The crimping equipment produces a crimping force, by which the contact is connectable with the conductor so as to be electrically and mechanically non-detachable.
2. Description of the Related Art
The tern "crimping" is internationally established and standardized in terms of technique. In practice, however, expressions such as pressing, squeezing, fixing or attaching are also used. Under crimping, there is understood the production of a non-detachable electrical and mechanical connection between a conductor and a contact. During the crimping operation, the material to be connected is permanently plastically deformed. Poorly conducting surface layers, if present, are broken up, which promotes the electrical conductivity. A correct crimping, however, also prevents the ingress of corrosive media even under more difficult operational conditions such as temperature change or vibration.
The object of the crimping is the production of a good mechanical and electrical connection which remains unchanged qualitatively over a long period of time.
For crimping, contact-specific crimping tools are used with a stationary crimping anvil below and vertically displaceable crimping dies above (see FIGS. 1 to 3). A wire crimper and an insulation crimper are mounted in the crimping tool and can mostly be set to the wire diameter or the insulation diameter independently of each other in a vertical direction by way of raster discs with different height cams. These settings directly influence the quality of the crimped connection.
In the case of open crimped contacts (FIGS. 4 and 5) the conductive feed takes place above the contact. The conductor, previously stripped of insulation, is usually positioned correctly for the crimping operation relative to the contact, simultaneously in a radial and an axial direction, by automatic devices. Due to a downward movement of the crimping die, the conductor is first lowered by means of a mechanical system into the upwardly open wire and insulation crimping claws. The actual crimping operation begins thereafter with reshaping of the straps according to the crimping die shapes. After the stroke of the crimping dye, the crimp has the intended pressed shape (FIG. 5), which is in turn dependent on the contact sheet metal used, the wire cross-section, the copper of the wire and the insulation stripping. When the contacts are closed, the crimping region, shaped as a tube, must be entered axially in a radial orientation.
A sectional diagram of a faultlessly executed crimped connection shows the originally individual round flexible wires of the conductor pressed compactly one against the other into polygons. An internal surface in the crimped region of the contact shows deformations of the contact points of the individual flexible wires. In the wire crimping, all individual wires must be encompassed. The individual wires must, according to respective cross-section, project by about 0.5 millimeters out at a front end of the wire crimp and may not disappear in the crimp. The conductor and the conductor insulation must be visible in a window lying between the wire crimp and the insulation crimp. The insulation crimp must encompass the insulation without penetrating thereinto.
Important criteria for judgement of a crimped connection are the shape of the crimp, the height of the crimp and the resistance to tearing-out of wires. These kind of criteria are suitable however only during the setting-up of a crimping machine and in the case of random samples during production. In order to meet present-day quality requirements for all crimped connections, means must be available, which can receive, evaluate and store crimping data about each crimped connection during the crimping process so as to influence machine data in dependence on the result. For the judgement of the crimped connection (without mechanical destruction of the crimped connection), the crimping force is related to crimping travel or to crimping time. By appropriate evaluation of the crimp data, the quality of a crimped connection can be reliably judged.
The process or the apparatus for the judgement of the quality of a crimped connection must recognize crimping faults, such as, incorrect insulation crimp height, incorrect wire crimp height, not encompassed flexible wires, wrong or no stripped insulation length, wrong laying-in depth, and flexible wires cut off during the insulation stripping. Corresponding fault reports must then be provided.
A method for the detection of missing flexible wires, or of crimped-in conductor insulation in a crimped connection, by reference a graph of the crimping force, is known from the reference EP 0 460 441. Value pairs, consisting of crimping force and the position of the crimping die are measured during a crimping operation and stored. The value pairs are plotted on a graph to show the crimping force of the crimping operation in dependence on the position of the crimping die. A curve section of the graph, with a strong rise in force, is linearized and a point is determined from the mean of the minimum and the maximum crimping force. The point is compared with a reference value. If the point lies within a predetermined deviation from the reference value, the crimped connection is judged to be of acceptable quality. During the evaluation of the graph of the crimping force of the crimping operation, the maximum crimping force is also taken into consideration. If the maximum crimping force deviates excessively from a second reference value, the crimped connection is rejected as unusable. The point in the curved section with a strong rise in force and the maximum crimping force yield information related to missing flexible wires or crimped-in conductor insulation in the crimped connection.
In a crimping press common in the market, a force sensor detects the force, which is stored in digital form as a force-dependent curve course, during the crimping operation. This course is compared with a reference curve. The type of crimping fault is deduced in accordance with the magnitude of the deviation from the reference curve.
It is a disadvantage of this known process and apparatus that no differentiated statement about the quality of the crimped connection is possible in spite of great expenditure for the computer, memory and computing.